1. Field of the Invention
The present invention relates to differential pressure/pressure transmitters, and in particular to pressure transmitters used for industrial measurement, having a construction in which an overpressure, even if applied to the pressure sensing assembly, is not transferred to the sensor itself, thus preventing sensor damage.
2. Description of the Prior Art
In the past, as a characteristic index of diaphragms adopted for differential pressure/pressure transmitters, xe2x80x9cf(xcfx86)xe2x80x9d has been conventionally used to indicate the characteristic of diaphragm displacement volume xe2x80x9cxcex94Vxe2x80x9d to pressure xe2x80x9cPxe2x80x9d. For this characteristic, it is desirable that the linear relationship have as uniform a slope as possible in a measuring pressure range.
A differential pressure transmitter adopting a center diaphragm having such an ideal characteristic becomes capable of obtaining output signals from the sensor proportional to the process pressures. The transmitter also enables measurement error to be extremely small, even if higher order terms in a higher order equation are neglected in signal conversion in the amplifier assembly and in corrective calculation in the CPU.
In the meantime, conventional differential pressure/pressure transmitters adopting a conventional three-diaphragm system, that is, comprising two process diaphragms on the high and low pressure sides and one center diaphragm inside the body, for a total of three diaphragms, have a construction in which the center diaphragm moves in both directions depending on the process pressures.
In such a construction, it is required to obtain the uniform linear characteristic xe2x80x9cf(xcfx86)xe2x80x9d. To obtain such a characteristic, it is effective to take a remedial measure such as increasing the outer diameter of the center diaphragm or making the thickness of the center diaphragm thinner.
However, the problem is mainly solved by increasing the diameter of the center diaphragm because making the thickness of the diaphragm thinner may cause greater stress to be generated.
In these differential pressure/pressure transmitters using such a three-diaphragm system, if an overpressure is applied to a process diaphragm on the high pressure side or the low pressure side, the process diaphragm on the pressure-applied side is closely pressed to the body.
This stops moving of the pressure transferring oil enclosed inside the body, then pressure transfer to the sensor assembly is lost, and the overpressure is not transferred to the sensor assembly.
As shown in FIG. 1 and FIG. 2, differential pressure/pressure transmitter 110 is composed of pressure detection assembly 111 that converts the pressure based on the pressure difference between high pressure and low pressure from a process and amplifier assembly 112 that comprises the electrical circuit to amplify signals generated in detection assembly 111.
Pressure detection assembly 111 is composed of a high pressure-side flange 113 forming the high pressure introducing part that introduces high pressures from a process, a low pressure-side flange 114 forming the low pressure introducing part that introduces low pressures from a process, and pressure sensing assembly 115 that detects both high pressure from high pressure-side flange 113 and low pressure from low pressure-side flange 114 using a diaphragm. High pressure-side flange 113 and low pressure-side flange 114 are fixed with nuts 116 and bolts 117.
Pressure sensing assembly 115, as shown in FIG. 2, has body 121 whose upper middle part is formed in the shape of a slender neck, sensor assembly 123 fixed in the center position of the upper part of body 121 using ring 122, high pressure-side diaphragm assembly 124 and low pressure-side diaphragm assembly 125 provided facing to the outside and positioned back to back to each other in the lower part of body 121.
Further, inside body 121, high pressure-side oil transfer hole 126 which transfers oil from high pressure-side process diaphragm assembly 124 to sensor assembly 123 and low pressure-side oil transfer hole 127 which transfers oil from low pressure-side process diaphragm assembly 125 to sensor assembly 123 are provided. Details of each part will be described below.
Sensor assembly 123 is composed of terminal 128, differential pressure sensor 129 that detects differential pressures by applying high pressure-side pressure from the top, and low pressure-side pressure from the bottom of the differential pressure sensor, and two hermetically sealed terminals 130a and 130b which are electrically connected to differential pressure sensor 129 by wire-bonding. The two hermetically sealed terminals 130a and 130b are connected to amplifier assembly 112 shown in FIG. 1.
There is a space between high pressure-side diaphragm assembly 124 and body 121, in which high pressure-side oil 133 is enclosed, and this space is connected with high pressure-side conducting hole 139 which leads to the space between center diaphragm C and body 121.
In addition, high pressure-side conducting hole 139 is connected to high pressure-side oil transfer hole 126. These spaces and holes are filled with high pressure-side oil 133 for pressure transfer.
Similarly, there is a space between low pressure-side diaphragm assembly 125 and body 121, in which low pressure-side oil 137 is enclosed, and this space is connected with low pressure-side conducting hole 142 which leads to the space between center diaphragm C and body 121.
Low pressure-side conducting hole 142 is also connected to low pressure-side oil transfer hole 127. These spaces and holes are filled with low pressure-side oil 137.
In differential pressure/pressure transmitter 110 having the above described structure, specifically in pressure sensing assembly 115, if high pressure-side diaphragm assembly 124, for example, receives pressure from a high pressure-side process, that pressure is transferred to high pressure-side oil 133 and the transferred pressure of high pressure-side oil 133 is supplied to differential pressure sensor 129 in sensor assembly 123 and center diaphragm C via high pressure-side transfer hole 126 after passing through high pressure-side conducting hole 139.
At the same time, if low pressure-side diaphragm assembly 125 receives pressure from the low pressure-side process, that pressure is transferred to low pressure-side oil 137 and the transferred pressure of low pressure-side oil 137 is supplied to differential pressure sensor 129 in sensor assembly 123 and center diaphragm C via low pressure-side transfer hole 127 after passing through low pressure-side conducting hole 142.
In such a manner, pressures from the high pressure-side and low pressure-side are transferred using oil 133 and 137, and their difference is detected with differential pressure sensor 129.
In this case, if a pressure difference is generated between the high pressure side and low pressure side and, for example, the pressure on the high pressure side becomes an overpressure as a result of loss of pressure balance between the high and low pressure sides, the process diaphragm of high pressure-side diaphragm assembly 124 moves towards body 121, and the center diaphragm C is also deflected corresponding to the volume of moved oil at that time.
Further, the low pressure-side oil also moves due to the deflection of center diaphragm C to push the process diaphragm of low pressure-side diaphragm assembly 125 towards the outside.
However, if a center diaphragm in the three-diaphragm system described in conventional techniques is employed, the stress generated in the center diaphragm becomes high and so there is a problem that a stronger material from the viewpoint of strength of material must be employed.
In addition, although it is required that the material itself has ductility for forming diaphragms, if a stress generated in the center diaphragm employed for differential pressure/pressure transmitters becomes high, a strong, non-ductile material is an indispensable requirement for the center diaphragm itself.
From the above description, center diaphragms supplied by conventional techniques cannot solve these conflicting problems because such strong diaphragms in material strength are hard and not ductile and thus difficult to be molded as center diaphragms.
Consequently, there is a problem to be solved so that the corrugated shape of the center diaphragm is improved, with which a large displacement volume is ensured even if the stress is small, that is, a larger volume is obtained by comparing moving volumes in the initial state of the center diaphragm and in the state of the pressure application to the center diaphragm.
The differential pressure/pressure transmitter concerning the present invention, in which the solutions to the above problems are achieved, is as shown below.
(1) A differential pressure/pressure transmitter provided with a high pressure-side diaphragm assembly comprising a high pressure-side process diaphragm, which transfers a high pressure from a process to the high pressure-side transfer oil, and a high pressure-side pre-loading diaphragm arranged so that its surface contacts the above high pressure-side transfer oil in addition to its back surface contacting closely the high pressure wetted surface having the low pressure-side overpressure liquid path;
a low pressure-side diaphragm assembly comprising a low pressure-side process diaphragm, which transfers a low pressure from the process to the low pressure-side transfer oil, and a low pressure-side pre-loading diaphragm arranged so that its surface contacts the above low pressure-side transfer oil in addition to its back surface contacting closely the low pressure wetted surface having the high pressure-side overpressure liquid path; and
a differential pressure sensor assembly which detects the pressure difference between the above high pressure-side transfer oil from the above high pressure-side diaphragm assembly and the above low pressure-side transfer oil from the above low pressure-side diaphragm assembly;
the above high pressure-side pre-loading diaphragm and low pressure-side pre-loading diaphragm further respectively comprising:
a center flat part obtained by forming the center position in a flat, disk shape,
a corrugated part obtained by forming the outside of the above center flat part in a corrugated shape so that the outside part of the above center flat part projects towards a plane contacting the above high pressure-side or low pressure-side wetted surface, and
an outer flat part obtained by flattening the section from the outside of the above corrugated part to the periphery.
(2) A differential pressure/pressure transmitter mentioned in (1), wherein the number of corrugations composing the above corrugated part is only one.
(3) A differential pressure/pressure transmitter mentioned in (1), wherein the number of corrugations forming the above corrugated part is two or more.
(4) A differential pressure/pressure transmitter provided with
a high pressure-side diaphragm assembly comprising a high pressure-side process diaphragm, which transfers a high pressure from a process to the high pressure-side transfer oil, and a high pressure-side pre-loading diaphragm arranged so that its surface contacts the above high pressure-side transfer oil in addition to its back surface contacting closely the high pressure wetted surface having the low pressure-side overpressure liquid path;
a low pressure-side diaphragm assembly comprising a low pressure-side process diaphragm, which transfers a low pressure from the process to the low pressure-side transfer oil, and a low pressure-side pre-loading diaphragm arranged so that its surface contacts the above low pressure-side transfer oil in addition to its back surface contacting closely the low pressure wetted surface having the high pressure-side overpressure liquid path; and
a differential pressure sensor assembly which detects the pressure difference between the above high pressure-side transfer oil from the above high pressure-side diaphragm assembly and the above low pressure-side transfer oil from the above low pressure-side diaphragm assembly;
the above high pressure-side pre-loading diaphragm and low pressure-side pre-loading diaphragm further respectively comprising:
a center flat part obtained by forming the center position in a flat, disk shape,
a corrugated part obtained by forming the outside of the above center flat part in a corrugated shape so that the height of the corrugation projected towards a plane contacting the above high pressure-side or low pressure-side wetted surface is higher than the height of the corrugation projected towards the opposite surface, and
an outer flat part obtained by flattening the section from the outside of the above corrugated part to the periphery.
(5) A differential pressure/pressure transmitter mentioned in (4), wherein the number of corrugations forming the above corrugated part is only one.
(6) A differential pressure/pressure transmitter mentioned in (4), wherein the number of corrugations forming the above corrugated part is two or more.
(7) A differential pressure/pressure transmitter provided with
a high pressure-side diaphragm assembly comprising a high pressure-side process diaphragm, which transfers a high pressure from a process to the high pressure-side transfer oil, and a high pressure-side pre-loading diaphragm arranged so that its surface contacts the above high pressure-side transfer oil in addition to its back surface contacting closely the high pressure wetted surface having the low pressure-side overpressure liquid path;
a low pressure-side diaphragm assembly comprising a low pressure-side process diaphragm, which transfers a low pressure from the process to the low pressure-side transfer oil, and a low pressure-side pre-loading diaphragm arranged so that its surface contacts the above low pressure-side transfer oil in addition to its back surface contacting closely the low pressure wetted surface having the high pressure-side overpressure liquid path; and
a differential pressure sensor assembly which detects the pressure difference between the above high pressure-side transfer oil from the above high pressure-side diaphragm assembly and the above low pressure-side transfer oil from the above low pressure-side diaphragm assembly;
the above high pressure-side pre-loading diaphragm and low pressure-side pre-loading diaphragm further respectively comprising:
a center flat part obtained by forming the center position in a flat, disk shape,
a corrugated part obtained by forming the outside of the above center flat part in a corrugated shape so that the curvature of the radially outer crest portion of the corrugations projected towards a plane contacting the above high pressure-side or low pressure-side wetted surface is larger than the curvature of the radially inner crest portion of the above corrugations, and
an outer flat part obtained by flattening the section from the outside of the above corrugated part to the periphery.
(8) A differential pressure/pressure transmitter mentioned in (7), wherein the number of corrugations forming the above corrugated part is only one.
(9) A differential pressure/pressure transmitter mentioned in (7), wherein the number of corrugations forming the above corrugated part is two or more.
(10) A differential pressure/pressure transmitter mentioned in (7), wherein the above described outer flat part is formed so that its radial dimension is larger by five times or more than the thickness of the pre-loading diaphragm.